Optical fiber technology is widely applied in communication, including telecommunication, data communication, and cable television. A high performance optical fiber system such as an optical fiber communication system desires that all optical modules employed in the system to be polarization insensitive. Optical performance and polarization insensitivity are competing goals. To achieve high performance, the optical modules in a high performance optical fiber system employ high performance optical materials. Unfortunately, many high performance optical materials are polarization sensitive. Techniques have been developed to construct polarization insensitive high performance optical modules with polarization sensitive high performance optical materials.
A popular technique to achieve polarization insensitivity in an optical module is to collimate the light entering the optical module through an optical fiber with an optical fiber collimator and then separate the collimated light beam into a first polarized light beam and a second polarized light beam with a polarizing beam splitter. The first and second polarized light beams are physically separated. The polarization of the first polarized light beam is orthogonal to the second polarized light beam. The polarization of either the first or the second polarized light beam is then rotated ninety degrees so that the first and second polarized light beams have the same polarization state. The first and second polarized light beams then enter the polarization sensitive section of the optical module, which may include polarization sensitive high performance optical materials. The polarization sensitive section of the optical module processes the first and second polarized light beams into first and second processed light beams respectively. When exiting the polarization sensitive section of the optical module, the polarization of either the first or the second processed light beam is rotated ninety degrees. After that, a second polarizing beam splitter combines the first and the second processed light beams into a single light beam. Then a second optical fiber collimator couples the single light beam to an optical fiber. One skilled in the art understands that the arrangement for processing the light from an optical fiber into two orthogonally polarized light beams with an optical fiber collimator and a polarizing beam splitter is identical to the arrangement for processing two orthogonally polarized light beams into a single light beam and couples the single light beam to an optical fiber with a polarizing beam splitter and an optical fiber collimator. The primary difference between the arrangements is the light propagation directions. One skilled in the art further understands that all physical optical components, including optical fiber collimator, collimating lens system, and beam splitter, may only substantially perform their intended function and unable to perform their intended function perfectly. Additionally, one skilled in the art may refer to the polarization state of a light beam as the polarization of the light beam. Because the first and second light beams have identical polarization when they pass through the polarization sensitive section of the optical module, the polarization sensitive section of the optical module processes them equally. Consequently. the optical module is polarization sensitive.
A commonly employed arrangement for collimating the light from an optical fiber and separating the collimated light beam into two orthogonally polarized light beams is shown in FIG. 1. The arrangement includes optical fiber collimator 103 and polarizing beam displacer 102 on baseplate 100. A polarizing beam displacer is a polarizing beam splitter that separates a light beam into two substantially orthogonally polarized parallel light beams that are physically separated. Referring to FIG. 1, an optical fiber collimator includes housing 101, collimating lens 114, and the end portion of optical fiber 111. At the end of optical fiber 111 is optical fiber termination 113. Fiber ferrule 112 provides structural support to optical fiber 111. Housing 101 holds fiber ferrule 112 and collimating lens 114. Collimating lens 114 collimates the light from optical fiber 111 through optical fiber termination 113 into a collimated light beam, which may have any polarization. Light path 120 of the collimated light beam is shown as the dot-dash line in FIG. 1. Beam displacer 102 separated the collimated light beam into a first and a second polarized light beam. Light path 121 and light path 122 are the light paths of the first polarized light beam and second polarized light beam respectively. The polarization of the first polarized light beam is substantially orthogonal to the polarization of the second polarized light beam. FIG. 1 shows that housing 101 directly and mechanically supports collimating lens 114 and fiber ferrule 112. and baseplate 100 directly and mechanically supports housing 101 and polarizing beam displacer 102. This arrangement can also be used to couple two orthogonally polarized light beams in an optical fiber. One skilled in the art understands that this arrangement has numerous applications besides the one stated above and there are numerous optical fiber collimator designs besides that shown in FIG. 1.
The above arrangement is commonly employed in optical modules. One of the steps in the fabrication process of the optical modules is to align the optical fiber collimator, the polarizing beam splitter, and other optical components in the optical modules. Align the optical fiber collimator, the polarizing beam splitter, and other optical components in the same step can be challenging because it involves aligning more than two optical components. It is desirable to integrate the polarizing beam splitter to the optical fiber collimator and align the two to form an integrated optical fiber collimator. By doing so, the number of optical components that require alignment in the fabrication of the optical module may be reduced and alignment process may be simplified. It is an object of this invention to provide an integrated optical fiber collimator that includes a built-in polarizing beam splitter.